That simple phrase is loaded with political baggage, and often accompanied by vague promises and complex jargon. Different candidates use it to target different voter blocs, leading to sometimes divergent, even contradictory ideas.

"People are talking about this as a goal, as a commitment, as a value as much as a specific program," said Celinda Lake, a Democratic pollster.

In championing "Medicare-for-all," politicians often put forth a general idea: universal health care, or some system in which everyone can afford medical care. But their visions for achieving that vary wildly.

Sometimes Medicare-for-all is meant to promise a single-payer health care system meaning everyone is covered by one, often government-run health plan. In other cases, politicians who say they support "for all" actually mean "for more."

Every proposal brings its own trade-offs.

"There's not just one easy answer to what a single-payer system would do to the United States," said Jodi Liu, an economist at the nonprofit RAND Corp. who studies single-payer proposals. "What happens depends on how that change is being designed, and how it's being implemented."

Here's a primer on the Medicare-for-all debate. Keep it in your back pocket: This argument won't be disappearing anytime soon.

Q: Isn't Medicare-for-all what it sounds like? Medicare for everybody?

A: Not quite. But also, kind of.

Politicians talking about Medicare-for-all typically mean one of two things. It's either a specific proposal in which every American is covered by the same, single health plan, or the general idea that anyone has the option to get health care through Medicare.

The first understanding is outlined in a bill from Sen. Bernie Sanders, I-Vt. Co-sponsors include Senate Democrats like Elizabeth Warren of Massachusetts, Kamala Harris of California, Cory Booker of New Jersey, Kirsten Gillibrand of New York and Jeff Merkley of Oregon. All but Merkley have announced a run for president.

And they are talking about this on the campaign trail.

Sanders' bill would outlaw private insurance where it competes with the public plan and change Medicare substantially by eliminating copays and other cost sharing, while expanding the program to cover long-term care, prescription drugs, dental care and vision. (As the bill is written, it's hard to see what would be left for private plans to cover.)

The program would phase in over four years and cover every American. And it's worth noting that, though many countries run a single-payer system, none offers all of those "expanded" benefits because the expense could be enormous. Also, many single-payer programs do require a degree of cost sharing, involving small copayments or deductibles.

In other cases, the "Medicare-for-all" phrase has been repurposed.

The midterms saw a wave of Democrats campaigning on it. But beyond the buzzwords, what they were actually talking about was lowering Medicare's eligibility age or giving people the option to buy in or join the program. This would leave the private insurance industry intact. It would also preserve Medicare Advantage, in which the government pays private companies to run Medicare plans.

For many voters, it's less about granular details and more about the principle, Lake suggested: "The highest level of support is when you talk about (Medicare-for-all) generally."

Q: So are Democrats saying we should get rid of private insurance?

A: Democrats who have signed on to Sanders' bill have endorsed legislation that would outlaw virtually all private health insurance. That's controversial.

Private insurance covers the largest share 56 percent in 2017 of Americans. And voters are often afraid of losing what they have if it's uncertain they'll get something better in exchange. Just ask then-President Barack Obama, whose Affordable Care Act-related promise that "if you like your plan, you can keep it" sparked sharp backlash after proving untrue.

This gets at a key question: Can Medicare-for-all advocates convince voters they'll replace their health plans with something better?

After all, most Americans say they support Medicare-for-all. But some of the same polls indicate that most people with employer-sponsored insurance think their coverage would be unaffected by the switch. That's false.

Critics also say eliminating private insurance could gut a major sector of the health economy. As of December 2018, private health coverage was directly responsible for almost 540,000 jobs, according to the Bureau of Labor Statistics. Economists note, though, that predicting how many jobs would go away versus how many could be absorbed by the new system is difficult, as is projecting any macroeconomic impact.

The magnitude of such a change underscores why some Democrats are trying to tread lightly for fear of land mines.

When probed on Medicare-for-all, Harris said she supported eliminating private insurance while also saying she would, in the interim, back other bills that expand access to health care. Warren, in a televised interview, sidestepped specifics altogether. And Booker told reporters he would not outlaw private health care, noting that many other countries have achieved universal coverage without taking this step.

For example, Germany has universal health care but leaves private insurance intact, while heavily regulating the industry and requiring plans be not-for-profit.

Q: So what other options are Democrats talking about?

A: Voters should get familiar with two other ideas: lowering Medicare's eligibility age, and the "public option," either through a Medicare or Medicaid buy-in.

These concepts are decidedly not Medicare-for-all think "Medicare for more" or "Medicaid for more."

Lowering the eligibility age loops more people into the current system and is seen by advocates as a potential step toward single-payer, said Alex Lawson, head of the left-leaning Social Security Works, who has been involved in drafting Medicare-for-all legislation.

The public option lets people purchase coverage through Medicare or Medicaid. It has attracted criticism from Democrats aligned with the Sanders wing, who argue it's settling for less.

Senate Democrats have introduced bills advancing such ideas including Merkley, who pushed a Medicare-based public option to let individuals and employers buy Medicare coverage, while also attaching himself to Sanders' measure. A proposal from Sens. Tim Kaine, D-Va., and Michael Bennet, D-Colo., would extend that option only to individuals. (Bennet is also purportedly weighing a 2020 bid.)

Said Liu, the health economist: "The devil is in the details."

Q: Shouldn't we consider who would pay? Would this make things better?

People would not pay what they currently do for health insurance, an outlay that's only getting more expensive. They would also likely get more generous health coverage. And lawmakers are pitching various other bills see Warren's wealth tax, Sanders' estate tax or the 70 percent marginal tax on the wealthy touted by Democratic New York Rep. Alexandria Ocasio-Cortez that backers argue would generate revenue to pay for something like Medicare-for-all.

Perhaps more significant, at least politically, are the implications for health care stakeholders like hospitals, insurers and drugmakers. All stand to lose under single-payer, especially if it's used to bring down health care costs. They're already working to make their opposition felt. (That said, opposition from the health industry is not universal.)

Q: When Democrats say they want Medicare-for-all, then do they really mean single-payer?

A: There has been a lot of brouhaha on this.

Take the backlash when Harris, after backing single-payer, said she also supported "Medicare-" and "Medicaid for more"-type policies. Her spokesman compared that to "wanting a burrito" while being willing to accept tacos in the meantime.

Of course, Harris isn't the only one to straddle those plans. Merkley, Gillibrand, Booker and Warren have put their names to multiple health reform bills. So, in fact, has Sanders, who voted to support, among other bills, the Affordable Care Act decidedly not single-payer.

Q: So are Democrats wavering? Is saying "Medicare-for-all," or even single-payer, a hook to win votes, or a bargaining strategy to end up with a public option instead?

A: It just isn't that simple.

"None of us can see into the hearts of anybody. And it's not a low-bar thing to sponsor a bill," said Lawson of Social Security Works. In a presidential campaign, though, "people will want to hedge."

But, he added, Medicare-for-all's popularity even as a concept shows something significant.

"There is a consensus that the current system needs to fundamentally transform," he said. "There's a commitment to do that. Then we have to argue out the details."

(Kaiser Health News (KHN) is a national health policy news service. It is an editorially independent program of the Henry J. Kaiser Family Foundation.)